1. Field of the Invention
Technology described herein relates to manufacture of semiconductor devices. More specifically, methods are described of forming field effect transistors using strained materials.
2. Description of the Related Art
Germanium was one of the first materials used for semiconductor applications such as CMOS transistors. Due to vast abundance of silicon compared to germanium, however, silicon has been the overwhelming semiconductor material of choice for CMOS manufacture. As device geometries decline according to Moore's Law, the size of transistor components poses challenges to engineers working to make devices that are smaller, faster, use less power, and generate less heat. For example, as the size of a transistor declines, the channel region of the transistor becomes smaller, and the electronic properties of the channel become less viable, with more resistivity and higher threshold voltages. Carrier mobility is increased in the silicon channel area by using silicon-germanium stressors embedded in the source/drain areas, as some manufacturers have done for the 45 nm node. For future nodes, however, still higher mobility devices are needed. Thus, there is a continuing need for methods and apparatus to form high mobility semiconductor devices.